Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$75.73	10.688%	$83.824	$83.82	$83.80	$83.80
Purchase #2	$152.83	10.489%	$168.8603	$168.86	$168.85	$168.90
Purchase #3	$210.38	8.576%	$228.4222	$228.42	$228.40	$228.40
Purchase #4	$39.63	7.324%	$42.5325	$42.53	$42.55	$42.50
Purchase #5	$49.95	3.290%	$51.5934	$51.59	$51.60	$51.60
Purchase #6	$128.59	7.387%	$138.0889	$138.09	$138.10	$138.10
Purchase #7	$96.25	11.794%	$107.6017	$107.60	$107.60	$107.60
7 purchase totals =	$753.36		$820.9230	$820.91	$820.90	$820.90